With PSARC/2008/755, the topic of "soft state" data association with
a device was raised. In the case log, there's discussion of whether
what is being stored is actually "soft state". I'll agree that soft
state should be per instance of a device but there's still a problem
here that we need to solve more genericly...
And that is allowing devices, especially those that want to be
CLONE_DEV devices, to store some per-open context, somewhere.
At present this is left up to the device driver writer, so using
mod_hash or similar with the minor number as a key is an easy
solution. But that is rather imposing...
What I'd like to suggest is that we consider expanding the entry
points for regular device drivers to allow for context to be created
in open(9e), passed back in with all of the other entry points (read,
write, strategy, etc) and require the driver to clear it in close(9e).
This would change function prototypes to be something like:
int prefixopen(dev_t *devp, int flag, int otyp, cred_t *cred_p, void
**ctxp);
int prefixread(dev_t dev, struct uio *uio_p, cred_t *cred_p, void *ctx);
int prefixclose(dev_t dev, int flag, int otyp, cred_t *cred_p, void **ctxp);
and so forth.
For existing drivers, not changing "ctxp" would result in NULL being
passed into the driver as the "ctx" pointer.
Thoughts?
Comments?
Flames?
Darren
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